In general, unlike primary batteries, secondary batteries are rechargeable, enabling repeated charge and discharge cycles. Secondary batteries are extensively used in advanced electronic appliances, such as cellular phones, notebook computers and camcorders.
Secondary batteries are classified into lithium secondary batteries, Ni—Cd batteries, and Ni-MH batteries. In particular, lithium secondary batteries operate at voltages of about 3.7 V, a voltage three times greater than that of Ni—Cd batteries and Ni-MH batteries, which are used as power sources for portable electronic appliances. In addition, lithium secondary batteries have high energy density per unit weight. For these reasons, lithium ion secondary batteries are being increasingly used in fields of advanced electronic technology.
Lithium secondary batteries are classified according to the type of electrolyte used. Lithium ion batteries use liquid electrolytes and lithium polymer batteries use polymer electrolytes. In addition, lithium secondary batteries can be manufactured in various shapes, for example cylinders and pouches.
Since lithium secondary batteries have high energy densities relative to other secondary batteries, electric and thermal insulation of the positive electrode from the negative electrode is very important. A typical electrode assembly in a lithium secondary battery includes a positive electrode plate, a negative electrode plate and a separator, which are wound to form a jelly-roll structure. The separator is positioned between the positive and negative electrode plates to insulate the positive electrode plate from the negative electrode plate. In addition, an electrode tab is connected to and extends from the electrode assembly and comprises an insulation tape for electrically insulating the electrode tab from the electrode assembly, the can, or the cap assembly.
The higher energy densities of lithium secondary batteries may cause heat-generation in the lithium secondary batteries during charging and discharging. In particular, heat is generated in a lithium secondary battery if the lithium secondary battery is overcharged, over-discharged or if the battery short circuits. Generally, the negative electrode plate is separated from the positive electrode plate such that an electrochemical reaction may occur between the electrode plates through the separator. Thus, the electrode assembly generates a large amounts of heat. In particular, the section of the electrode assembly to which the electrode plate and the electrode tab are welded contacts different metals, causing the internal resistance in the section to increase, thereby generating large amounts of heat. For this reason, an insulation tape comprising resin is attached to the section between the electrode tab and the separator to prevent damage to the separator from the heat.
As the capacity of the lithium secondary battery increases, so does the energy density. Thus, heat may frequently be generated in the lithium secondary battery, causing battery malfunction, such as a short circuit. Since the insulation tape or the adiabatic tape used for electrical or thermal insulation mainly comprises organic materials, such as PI (polyimide), PET (polyethyleneterephthalate) or PP (polypropylene), the heat generated in the lithium secondary battery may decrease the thermal or electric insulation characteristics of the insulation tape.